Organic redox-active carbonyl-based polymers are intensively explored as promising high-capacity cathode materials for lithium and sodium batteries. In spite of many inspiring reports that appeared in the field, practical implementation of this group of materials is restricted severely by their poor operational stability. In the present report, we address the capacity fading problem in the recently reported lithium-polyimide batteries. We show experimentally that cathode degradation becomes less pronounced at high charge/discharge current rates, suggesting the involvement of some intermediate redox species in the failure process. Replacing a standard liquid electrolyte with the polymer formulation entirely suppresses the degradation and results in a stable battery performance over 800 cycles. DFT calculations have revealed that the investigated polyimide undergoes fragmentation to low molecular weight species via the rupture of N–N bonds in the main polymer chain during lithiation. Strong 3D coordination bonding involving Li, O, and N atoms preserves the integrity of the cathode structure, which can undergo reversible transition to the initial polymeric state and restore the N–N bonds between the repeating units during lithium removal upon oxidation. However, solvation of the intermediate low molecular weight species results in their disintegration from the cathode composite leading to capacity fading of the battery. The achieved insight into the electrochemical behavior of the investigated model polyimide structure provides very useful guidelines for designing novel cathode materials with enhanced stability with respect to electrochemical lithium (or sodium) insertion.

The results of a quantum-chemical study of the reactivity of fullerene C₆₀ in such reactions as polymerization (dimerization), cycloaddition, addition of valence-saturated molecules are presented. The mechanisms of these reactions are also discussed.

In this article, the specific features of competitive ionic and molecular transport in nanocomposite systems based on network membranes synthesized by radical polymerization of polyethylene glycol diacrylate in the presence of LiBF₄, 1-ethyl-3-methylimidazolium tetrafluoroborate, ethylene carbonate (EC), and TiO₂ nanopowder (d~21 nm) were studied for ¹H, ⁷Li, ¹¹B, ¹³C, and ¹⁹F nuclei using NMR. The membranes obtained were studied through electrochemical impedance, IR-Fourier spectroscopy, DSC, and TGA. The ionic conductivity of the membranes was up to 4.8 m Scm⁻¹ at room temperature. The operating temperature range was from −40 to 100 °C. Two types of molecular and ionic transport (fast and slow) have been detected by pulsed field gradient NMR. From quantum chemical modeling, it follows that the difficulty of lithium transport is due to the strong chemisorption of BF₄^– anions with counterions on the surface of TiO₂ nanoparticles. The theoretical conclusion about the need to increase the proportion of EC in order to reduce the influence of this effect was confirmed by an experimental study of a system with 4 moles of EC. It has been shown that this approach leads to an increase in lithium conductivity in an ionic liquid medium, which is important for the development of thermostable nanocomposite electrolytes for Li//LiFePO₄ batteries with a base of lithium salts and aprotonic imidasolium ionic liquid.

Elementary processes of electro mass transfer in the nanocomposite polymer electrolyte system by pulse field gradient, spin echo NMR spectroscopy and the high-resolution NMR method together with electrochemical impedance spectroscopy are examined. The new nanocomposite polymer gel electrolytes consisted of polyethylene glycol diacrylate (PEGDA), salt LiBF₄ and 1—ethyl—3—methylimidazolium tetrafluoroborate (EMIBF₄) and SiO₂ nanoparticles. Kinetics of the PEGDA matrix formation was studied by isothermal calorimetry. The flexible polymer–ionic liquid films were studied by IRFT spectroscopy, differential scanning calorimetry and temperature gravimetric analysis. The total conductivity in these systems was about 10⁻⁴ S cm⁻¹ (−40 °C), 10⁻³ S cm⁻¹ (25 °C) and 10⁻² S cm⁻¹ (100 °C). The method of quantum-chemical modeling of the interaction of SiO₂ nanoparticles with ions showed the advantage of the mixed adsorption process, in which a negatively charged surface layer is formed from Li⁺ BF₄^— ions on silicon dioxide particles and then from ions of the ionic liquid EMI⁺ BF₄⁻. These electrolytes are promising for use both in lithium power sources and in supercapacitors. The paper shows preliminary tests of a lithium cell with an organic electrode based on a pentaazapentacene derivative for 110 charge–discharge cycles.